1. Field of the Invention
This invention relates to a conductive composition, and more particularly, to a conductive composition which is an organic composition such as a conductive resin composition and a coating composition. Still more particularly, it relates to a conductive resin composition used in the form of a compound, paste, molded product, putty or the like, particularly in the field concerning semiconductors, covering a vast range including materials used for packaging, storage and transportation for the purpose of preventing electrostatic destruction, floorings used for prevention of electrostatic charging or removing electrostatic charges, shielding materials used for preventing electromagnetic wave hindrance, wire coating compositions used for preventing corona discharge deterioration, and synthetic resin thermisters.
This invention also relates to a highly conductive resin composition, which is used in the form of a paste, putty, coating composition, compound, pellets, molded product, sheet, film or the like and applied in the field covering a wide range, particularly in the field in which both a high conductivity and a high plasticity are required, including circuit wiring, take-out of electrodes, electrical contacts, plastic electrodes, conductive coating compositions, conductive films, surface heater elements, conductive plastics, conductive rubbers, conductive tires, connecter gaskets, electromagnetic shielding materials, antistatic materials, and wire coating compositions for preventing corona discharge.
This invention further relates to a method of making a conductive resin composition useful for forming a conductive resin film, and more particularly to a method of making a conductive resin composition that can be formed into a sheet, film, paste, coating composition or the like and used in antistatic materials or conductive coating compositions used for electrostatic coating.
This invention still further relates to a conductive composition utilized in an electrophotographic photosensitive member, and more particularly to a conductive composition used to obtain an improved conductive layer, conductive support or protective layer.
2. Description of the Prior Art
As materials or fillers compounded into a resin to impart the resin an electrical conductivity, metals such as silver, copper, aluminum, nickel, palladium and iron, metallic compounds such as silicon carbide, tin oxide, indium oxide and zinc oxide, and non-metals such as carbon are used in a crystal or amorphous and flaky, powdery or fibrous form. To obtain high and stable conductive compositions using these fillers, it is important for these fillers to be uniformly dispersed in a resin. For this end, the above powdery or flaky materials have been required to be, for example, pulverized to have finer particles, or made to have a smaller thickness, respectively, and the fibrous materials, to be made to have smaller diameter. However, particularly in the instance of metallic fillers, the fillers are affected by moisture or oxygen in the course of the above treatment or storage to give an oxide film produced on the surface, so that it is often difficult to obtain the desired electrical conductivity even if they are dispersed in a good state. Other compounds may similarly be often adversely affected by hydrolysis. In the instance of chemically stable compounds or fibrous materials, only a small effect can be obtained in taking the means for making them finer, e.g., in carrying out pulverization or the like. This requires a special mans for making them finer and also results in an increase in treatment cost. For these reasons, there is a limit in making particle size smaller or making materials finer in a preferable state, for the purpose of their dispersion in resins, so that materials with relatively course size have had to be used as they are. This consequently causes separation of resin from the filler after they have been compounded, tending to give a heterogeneously dispersed state and also often resulting in difficulty in long-term maintenance of electrical conductivity. In particular, it has often occurred that no desired electrical conductivity can be attained unless the materials are charged in a large amount.
On the other hand, it is also well known to use particulate, flaky or fibrous conductive or non-conductive fillers of various types whose surfaces are coated with conductive materials comprising a metal or a metal oxide such as indium oxide or tin oxide.
In regard to the conventional conductive resin compositions, they have so a large amount of filler component that the resulting resin composition necessarily has a small amount of resin component, resulting in a deterioration of various excellent properties inherent in resins. Such deterioration includes a lowering of mechanical strength, a lowering of flexibility, an increase in the density of a composition, a difficulty in molding, a decrease in glossiness, and an increase in cost because of the use of a large amount of expensive fillers.
In regard to the conductive coating compositions, the addition of a large amount of the metallic conductive materials such as copper, aluminum, iron and nickel brings about a lowering of the mechanical properties of coatings, and also the copper, aluminum, iron, etc. have had the disadvantages such that the electrical conductivity is lowered because of the formation of an oxide layer on the surface and the coatings are deteriorated because of copper or iron oxides. Now, inexpensive and highly stable carbon black has been hitherto used, but ths is accompanied with the disadvantage that hues are limited.
To discuss next the electrophotographic photosensitive member, it is fundamentally comprised of a support and provided thereon a photosensitive layer. The support more takes the form of a cylinder than the form of a sheet. This is because the jointless construction of the cylinder is advantageous for the continuous repeated application of charging, exposure, developing, fixing and destaticizing in the electrophotographic process.
In recent years, development has been remarkably made on electrophotographic printers that employ laser beams. Used as the electrophotographic photosensitive member used in laser beam printers are inorganic photosensitive members comprising selenium, cadmium sulfide or amorphous silicon and organic photosensitive members comprising polyvinyl carbazole, oxadiazole or phthalocyanine.
As laser beam sources, argon or helium-neon gas lasers have been hitherto used, but semiconductor lasers are recently used for the purpose of making apparatus more compact, more lightweight and more inexpensive. Taking account of the copying speed, resolution, and lifetime of the semiconductor laser, a reversal development system is also proposed in which a toner is adhered on the exposed area having a low potential.
However, because of the wavelength of the semiconductive laser, which is in the infrared region of from 700 to 850 nm, the above photosensitive member has so a low light-sensitivity in this wavelength region that this has been undesirable from a practical viewpoint. Now, several sensitizing methods are proposed. Known as the most effective method is to provide a functionally separated photosensitive layer comprising a lamination of a charge generation layer and a charge transport layer. The charge generation layer should preferably be a thin film because a greater part of the amount of exposure is absorbed in the charge generation layer to produce a large number carriers and also because the carriers thus produced must be injected into the charge transport layer without the recombination and trapping. Thus, from the viewpoints of the copying speed, resolution and lifetime of the semiconductive laser, the reversal development system in which a toner is adhered on the exposed area having a low potential is now prevailingly used.
In instances in which the semiconductor laser is used as a light source, however, no problem arises in line images such as letters or the like, but interference bands appear in halftone solid images. This is caused by the charge generation layer which is formed of a thin film as mentioned above, where the light that should have been absorbed in this layer is not absorbed in its entirety and reflects in part on the surface of the support, resulting in interference between this reflected light and the light reflected on the surface of the photosensitive layer.
Incidentally, in instances in which the material for the support comprises an insulating material such as paper or plastics, a conductive film must be formed on the support so that the charges can be immediately let off. In instances in which the support comprises a metal such as aluminum, copper, zinc, tin, stainless steel, brass or chromium, the conductive film may not be formed but, when an ordinary development system is taken, electrical failure of the photosensitive layer, or irregularities, scratches or defects on the conductive support come out as white dots in solid black on an image. When the reversal development system is taken, they come out as black dots in solid white on an image. These are great problems in both cases.
Now, to solve these problems, it is effective to provide a resin layer between the support and photosensitive layer. This resin layer must be a layer with an electrically sufficiently low resistivity, and should preferably be a resin layer having an electrical conductivity, which is usually called a conductive layer. The conductive layer is required to be not attacked by a solvent used in a coating solution for a coating formed thereon, and methods are known in which a cationic, anionic or nonionic electrolyte, or a polymeric electrolyte such as a quaternary ammonium salt or sulfonate is added in a hydrophilic resin or alcohophilic resin such as polyvinyl alcohol, ethyl cellulose, casein, gelatin or starch (for example, Japanese Patent Publications No. 56-54631 and No. 58-1772, Japanese Laid-open Applications No. 57-138990 and No. 59-121343). This layer, though depending on the degree of the irregularities, scratches or defects of the support, is not effective when it is a thin film, and thus required to be a film with a thickness of not less than 5 .mu.m.
It is also important for the electrophotographic photosensitive member to have moisture resistance, durability, and cleaning resistance. It is also important for its electrical resistance not to be affected by changes in use environments, in particular, changes in humidity. Under conditions of a low humidity of 10.degree. C./20% in winter seasons, it may follow that the electrical resistance increases to cause fog in the case of the ordinary developing system and cause a lowering of image density in the case of the reversal development system. On the other hand, under conditions of a high humidity of 30.degree. C./80% in rainy seasons, the electrical resistance may decrease to tend to cause the injection of charges from the support, resulting in the appearance of white dots in solid black on an image in the case of the ordinary development system, and black dots in solid white on an image in the case of the reversal development system.
To cope with the changes in use environment, a method is proposed in which the photosensitive member is heated with a heater built in the photosensitive member to effect dehumidification (for example, Japanese Laid-open Applications No. 55-96975 and No. 58-31344). This method, however, brings about an increase of an electric power and an increase in the apparatus cost, and is not preferred.
Incidentally, in the course of electrophotographic process, the photosensitive member is usually repeatedly used, so that charge deterioration, exposure deterioration, ozone deterioration, scratches due to toner, etc. may occur in the vicinity of the surface of the photosensitive member, resulting in an impairment of the lifetime of the photosensitive member. Now, a method is available in which a protective layer is further provided on the photosensitive layer. This protective layer is proposed to comprise polyester resin, urethane resin, polyvinyl butyral resin, phenol resin, cellulose acetate, a styrene/maleic anhydride copolymer, a polyamide, or the like (for example, Japanese Patent Publications No. 51-15748, No. 52-24414, No. 56-34860 and No. 56-53756). This method, however, can not be said to be satisfactory from the viewpoints of adhesion to photosensitive layers, scratches, durability such as slide resistance, environment resistance stability, etc.
As properties required in the conductive layer of the electrophotographic photosensitive member, it is also important for it not to be affected by changes in use environment, in particular, changes in humidity, as having been discussed in the above. When the conductive layer based on ion conduction is used, under conditions of a low humidity of 10.degree. C./20% in winter seasons, it may follow that the electrical resistance increases to cause fog in the case of the ordinary developing system and cause a lowering of image density in the case of the reversal development system. On the other hand, under conditions of a high humidity of 30.degree. C./80% in rainy seasons, the electrical resistance may decrease to tend to cause the injection of charges from the support, resulting in the appearance of white dots in solid black on an image in the case of the ordinary development system, and black dots in solid white on an image in the case of the reversal development system.
To cope with this, proposed are a method in which a metal deposit film or metallic coating is applied or a metallic foil is wrapped around as a conductive layer that has no humidity dependence and may not bring about neither an increase in the electrical resistance nor the interference bands even if the film thickness is made larger (for example, Japanese Laid-open Application No. 55-124152), a method in which a metallic powder of nickel, copper, silver, aluminum or the like is dispersed in a binder resin (for example, Japanese Laid-open Application No. 56-158339), a method in which carbon black is dispersed in a binder resin (for example, Japanese Laid-open Applications No. 50-25303 and No. 52-113735), and a method in which ZnO doped with Al or In, TiO.sub.2 doped with Ta, SnO.sub.2 doped with Sb or Nb, or ZnO, TiO, TiO.sub.2, SnO.sub.2, Al.sub.2 O.sub.3, In.sub.2 O.sub.3, SiO.sub.2, MgO, or a composite metal oxide of any of these is dispersed in a binder resin (for example, Japanese Laid-open Applications No. 55-146453, No. 56-143443, No. 58-217941 and No. 59-84257).
Also proposed is a method in which a conductive support comprising an insulating material such as paper or plastics filled with carbon or fiber of a metal such as aluminum, copper, brass, stainless steel or zinc (for example, Japanese Laid-open Applications No. 56-66854, No. 59-15600 and No. 59-97151).
In the instance in which the metal deposit film is applied, the method has the disadvantages that a batch system must be employed and moreover gas generates from the support, or it takes a long time to attain a film thickness without pin holes.
In the instance in which the metallic coating is applied, the method has the disadvantages that a primer treatment is required and it is difficult to maintain and control a plating bath.
In the instance in which the metallic foil is wrapped around, the method has the disadvantage that it is difficult to wrap around it with a good precision, using an endless metallic foil so that no joint area may be formed.
In the instance in which ZnO doped with Al or In, TiO.sub.2 doped with Ta, SnO.sub.2 doped with Sb or Nb, or ZnO, TiO, TiO.sub.2, SnO.sub.2, Al.sub.2 O.sub.3, In.sub.2 O.sub.3, SiO.sub.2, MgO, or a composite metal oxide of any of these is dispersed in a binder resin, a conductive layer having superiority as to environment dependence can be obtained. The method, however, has the disadvantages that since the above metallic powders or metallic oxides are insoluble to the binder resin and solvent in a coating solution and are in a bulky form and also the electrical conductivity is based on electron conduction, an area locally having a different resistance may be formed and no stable conductive layer may be obtained unless they are added in a large amount, and that because of their specific gravity which is as large as 3 to 8 they tend to be sedimented when they are dispersed in the coating solution, so that the operability becomes poor and no stable conductive layer can be obtained.
In the instance in which the material is filled with carbon, there are the disadvantages that the photosensitive member has the nature of injecting free carriers into the photosensitive layer, an area locally having a different resistance may be formed and no stable conductive layer may be obtained unless it is added in a large amount, and the thixotropy is so high that operability can be achieved with difficulty.
In the instance in which the material is filled with metallic fiber, there can be obtained a superior mechanical strength, slidability and electrical conductivity in the longitudinal direction. However, the method has the disadvantages that no stable mechanical strength, slidability and electrical conductivity can be obtained in the film thickness direction unless it is added in a large amount, and the adhesion can be little improved even if it is added in a large amount.
Incidentally, whiskers are meant to be beard-like single crystals, and refer to single crystals having a length not less than several times the average diameter. Linear-fibrous whiskers of potassium titanate, silicon carbide, silicon nitride, etc. are known in the art, and those to which electrical conductivity has been imparted are commercially available. Of these, a method in which a plastics filled with whiskers of potassium titanate is used in a conductive support is proposed in Japanese Laid-open Application No. 59-97152. Like the metallic fiber, there can be obtained a superior mechanical strength, slidability and electrical conductivity in the longitudinal direction because of the linear-fibrous form of the whiskers, but no stable mechanical strength, slidability and electrical conductivity can be obtained in the film thickness direction unless it is added in a large amount, and the adhesion can be little improved even if it is added in a large amount.
In regard to the electrophotographic photosensitive member employing the protective layer, a method is proposed in which a protective layer comprising fine powder of fluorine resin, silicone resin, polytetrafluoroethylene, polyethylene, polyethylene terephthalate or the like dispersed in a binder resin is used so that the durability such as slide resistance can be improved (for example, Japanese Laid-open Applications No. 52-117134, No. 55-25059, No. 56-25746 and No. 59-220743). The method disclosed in these can achieve a superior durability but has the disadvantages that the electrical resistance is so high that it remains as residual potential to cause fog in the case of the ordinary development system, and bring about a lowering of image density in the case of the reversal development system, and also that methods of preparing photosensitive members may be limited because of the materials insoluble to solvents.
For the purpose of not causing the fog as a result of an increase in residual potential, a method is also proposed in which a Lewis acid such as 2,4-dinitrobenzoic acid, phthalic anhydride, 2,6-dinitro-p-benzoquinone or p-bromanil is added in the protective layer so that a relatively slight trap may be formed without trapping of charges at the interface between the protective layer and photosensitive layer (for example, Japanese Laid-open Applications No. 53-133444 and No. 55-157748). There, however, may arise the problem that the durability such as scratch resistance and slide resistance are lowered.
Hence, an excessively low resistance of the protective layer results in the movement of charges in the lateral direction to cause a lowering of electrostatic charge potential. On the other hand, an excessively high resistance results in the accumulation of charges to increase residual potential, so that it is necessary to control the resistance of the protective layer to a suitable value and also make the resistance stable to the changes in use environment such as temperature and humidity. In addition, the protective layer must have a film thickness which is relatively thin to the extent that it may not substantially affect the resolution of the photosensitive layer, and also must be excellent in the durability such as scratch resistance and slide resistance.
Now, proposed is a method in which a protective layer comprising a metallic oxide dispersed in a binder resin (for example, Japanese Laid-open Applications No. 57-30845, No. 58-121044 and No. 59-223445). This method can obtain a photosensitive member free from charge accumulation accompanying repeated use and stable even to the changes in use environment. Since, however, the metallic oxide contained in the binder resin is insoluble to the binder resin and solvent and is in a bulky form, the optical characteristics may differ depending on the state of dispersion thereof even when it is contained in the protective layer in a constant amount. For example, the presence in the protective layer, of relatively large particles or of agglomerates because of non-uniform state of dispersion results in a lowering of the transparency of the protective layer to cause a lowering of the light-sensitivity of the photosensitive member and a lowering of image quality.
Incidentally, as previously mentioned, whiskers are meant to be beard-like single crystals, and refer to single crystals having a length not less than several times the average diameter. Linear-fibrous whiskers of potassium titanate, silicon carbide, silicon nitride, etc. are known in the art, and those to which electrical conductivity has been imparted are also commercially available. These can achieve a superior mechanical strength, slidability and electrical conductivity in the longitudinal direction, but no stable mechanical strength, slidability and electrical conductivity can be obtained in the diameter direction, i.e., the film thickness direction unless it is added in a large amount. If for that reason they are added in a large amount, the sensitivity of the photosensitive layer may be lowered because of a lowering of the transparency of the protective layer and moreover the adhesion can be little improved even if it is added in a large amount.